Abnormalities of opsonophagocytosis is the major predisposing cause in the vast majority of infections in high risk surgical patients such as following severe trauma, burn injury or renal transplantation. The present proposal will examine the potential benefit of several methods to improve host resistance to infection in such patients. Specifically, the immunopotentiator, C. parvum, will be given to patients with severe burn injury and to patients with renal allografts with and without complicating infections under carefully controlled conditions. Numerous variables of host resistance will be monitored. Another controlled study will examine the influence of increased dietary protein on host resistance mechanisms and infections in severely burned patients. The role of various opsonins in defense against specific pathogens will be examined in vitro and in animal models. Also, complement metabolism and an immunosuppressive factor generated by complement activation will be studied in animals. Finally, the potential benefit of selective nutritional therapy and of passive plasma therapy will be examined in appropriately deficient animals.